This invention relates to a new and useful improvement in multi-flapper check valves.
In flapper valves of the design disclosed in Bravo, U.S. Pat. No. 1,238,878 (1917), and improved upon by Wheeler in U.S. Pat. Nos. 3,007,488 (1961), 3,026,901 (1962), 3,072,141 (1963), and 3,074,427 (1963), the two flappers are urged toward their seated positions by one or more helical springs wound about a shaft, with the two ends of each spring contacting the two valve flappers respectively. Thus, both flappers are urged toward their seated position by the same spring; or, in the case of multiple spring use, each spring acts upon both flapper elements.
Because of the disparity between the frictional resistances of the two flappers of the check valve of the Wheeler design, and other differences in the forces acting on them, there is a tendency for one of the flappers to close more readily and therefore seat before the other. When one flapper has seated, and the other flapper has almost seated, the energy of a spring acting upon both flappers has been largely dissipated and the torque the spring exerts against the partially open flapper is relatively low. This can cause the flapper to hesitate before closing, resulting in possible pressure surges and hammer.
In Smith, U.S. Pat. No. 3,384,112 (1968), the inventor interconnected the flappers by a relatively complex gearing arrangement to promote synchronous flapper closure. The present invention involves a much less complicated adaptation of the basic valve structure to improve performance. Additionally, the present invention, by proper choice of relative spring strengths, allows for a design in which the flappers close synchronously, or one flapper closes before the other.
For improved valve response, it is desirable to increase the spring torque exerted against each flapper element as the flappers closely approach their seat. Accordingly, it is an object of the present invention to provide a multi-flapper check valve with improved valve response.
Another object of this invention is to provide a multi-flapper check valve wherein total angular spring deflection is reduced.
A further object of this invention is to provide a multi-flapper check valve wherein higher torque springs may be used to increase the torque acting upon a flapper when the flapper is near its seated position.
Yet a further object of this invention is to provide a multi-flapper check valve wherein each flapper is biased by a separate spring.
Other objects and purposes of this invention will appear from the following descriptions, examples, and claims.